1. Field of the Invention
The present invention relates to an optical storage apparatus for optically recording and reproducing information to/from an exchangeable medium such as an MO cartridge or the like. More particularly, the invention relates to an optical storage apparatus for suppressing a waveform fluctuation occurring in a tracking error signal each time a laser beam passes an ID portion of a medium track during an on-track control.
2. Description of the Related Arts
Attention is paid to an optical disk as a storing medium as a core of multimedia which has rapidly been developing in recent years. For example, as for an MO cartridge of 3.5 inches, in addition to a conventional MO cartridge of 128 MB, media of a high density recording of 230 MB, 540 MB, and 640 MB have also been provided in recent years. In an optical storage apparatus known as an optical disk drive using such an MO cartridge medium, when a write command or a read command is received from an upper apparatus, a seek control for positioning a laser beam to a target track designated on the medium is executed and the laser beam is pulled in. Subsequently, an on-track control for allowing the laser beam to trace a track center on the basis of a tracking error signal is performed and a writing or reading operation based on a command from the upper apparatus is executed. The on-track control is performed in a manner such that the tracking error signal indicative of a deviation amount from the track center is sampled and read as a digital signal value by an A/D converter every predetermined time, an actuator mounted on a carriage is driven to set an error between a target position showing the track center and the present position to zero, and the position of the laser beam is feedback controlled. When the laser beam passes an ID area constructed by emboss pits arranged at regular intervals on the medium tracks during the on-track control, there is a phenomenon such that a level fluctuation occurs in the tracking error signal. For the fluctuation of the tracking error signal caused by the return light of the ID area, when the signal value sampled by the A/D converter is transmitted through a PID filter, gains of P and D terms or a gain of a D term is reduced from a normal gain by a DSP which executes the on-track control, and a tracing response speed to a sudden level change in the tracking error signal due to the ID area is made dull, thereby preventing the fluctuation of the tracking error signal caused by the return light of the ID area from being added as a disturbance. The suppression of the level fluctuation of the tracking error signal caused by the ID area is basically performed by dropping the gain of the PID filter and making a servo response speed dull. When the gain of the PID filter is dropped, however, since the traceability of the servo becomes dull also with respect to a detection component of an inherent deviation amount included in the fluctuated tracking error signal from the track center, there is naturally a limit for the reduction in the filter gain. Consequently, the suppression of the level fluctuation of the tracking error signal caused by the ID area becomes insufficient and there is a problem that the on-track control becomes unstable. Since the suppression of the level fluctuation of the tracking error signal caused by the ID area is insufficient, there is also another problem such that the signal level exceeds an off-track slice level set for offtrack detection and the off-track is erroneously detected.